Peristaltic pumps are used to transfer liquids, gel, and semi-solids in many industries worldwide. These pumps have many advantages over other pumping methodologies such as they are easy to setup, and allow minimal contamination of transferred materials. Peristaltic pumps operate by squeezing elastic tubing in one direction. The repeated discharge and vacuum of the fluid to be transferred moves the fluid.
The peristaltic pump was designed to prevent contamination because no contact with the material being transferred is made with the exterior of the tubing. Existing peristaltic pump technologies also have a common set of problems: non-steady flow or pulsations, high flexible tube wear, high maintenance costs and not highly accurate metering of pumped volumes. The pump design of the present invention addresses these issues with new head designs that minimize these issues by using new materials and tube routing. A single roller manufactured with unique nonmetallic materials increases pump efficiency and minimizes tube wear. The tube layout minimizes pulsation and enables precise metering of pumped materials.
Back pressure is generated in the area where two tubes are pinched by rollers. This is the problem of pulsation that can damage fittings, piping and other system components connected at the output line. This pinched area makes dose control difficult. When rollers rotate in one direction, tension in the tube hose is forced to accumulate in one direction. This results in the problem of shorter lifetime of hose sections. In addition, friction between hose and roller is one of the factors that reduce lifetime of hose during operation. In addition, metal cast rollers with high thermal conductivity can damage the hose by the heat of friction. In addition, more energy and speed is required to drive a big outer roller by smaller inner bearings.
The amount of squeeze applied to the tubing affects pumping performance and the tube life—more squeezing decreases the tubing life dramatically, while less squeezing can cause the pumped medium to slip back, especially in high pressure pumping, and decreases the efficiency of the pump dramatically and the high velocity of the slip back typically causes premature failure of the hose. Therefore, this amount of squeeze becomes an important design parameter.
Increasing the number of rollers doesn't increase the flow rate, instead it will decrease the flow rate somewhat by reducing the effective (i.e. fluid-pumping) circumference of the head. Increasing rollers does tend to decrease the amplitude of the fluid pulsing at the outlet by increasing the frequency of the pulsed flow.
The length of tube (measured from initial pinch point near the inlet to the final release point near the outlet) does not affect the flow rate. However, a longer tube implies more pinch points between inlet and outlet, increasing the pressure that the pump can generate.
The bar is a metric (but not SI) unit of pressure, defined by the IUPAC as exactly equal to 100,000 Pa. It is about equal to the atmospheric pressure on Earth at sea level, and since 1982 the IUPAC has recommended that the standard for atmospheric pressure should be harmonized to 100,000 Pa=1 bar 750.0616827 Torr. The same definition is used in the compressor and the pneumatic tool industries (ISO 2787).
The main issues with existing designs are as follows:
1. Existing rollers/shoes element scrub the transfer tube with forces that stretch the tube and require the tube to be anchored to the pump housing to keep it from migrating out of the pump head.
2. Existing rollers/shoes element design requires frequent lubrication due to friction. It causes friction and heat generation, eventually leading to maintenance and replacement.
3. Existing transfer a pulsation energy to the tube anchors and downstream components of the system that cause stress and eventual wear. This is caused by the pump occluding mechanism where the rollers/shoes element loses contact with the tube. This results in a pressure release. When the roller regains contact with the tube, a pressure increase occurs causing significant pulsing of the material flow and tubing vibration.
4. Tube stretching changes the inner diameter of the tube which changes the material volume through the tube. Periodically the pump must be calibrated to compensate for this varied tube shape.
In U.S. Pub. No. US2006/024596, a compensating volume of fluid is defined between occluding members, but nothing prevents pulsation between loop input and output and fluid input port and output port. The use of 3 members still create 3 pulsations when occluded. Their design of occluding members permit friction between occluding members and tube. This stretches the tube, and changes it's shape resulting in changed volume. This is unacceptable in applications that require maintaining a constant volumetric flow rate. In addition, many components are used in this complicated structure, giving rise to a higher potential for mechanical failure caused by wear. The system also needs frequent lubrication of the numerous moving parts. Finally, a complicated design of drive assembly makes it difficult to replace tube that, increasing maintenance time and cost.
In US Pub. No US2012/0156074, the stator and rotor does not eliminate friction, therefore the use of hose clamps at the inlet and outlet prevent tube slippage. However, during continuous rotation of the pump, the tube will be stretched and made thinner at the side of the tube. Also this patent does not address the 3 pulsations by 3 rotors and wide pulsation between pump input hose and output hose.
In U.S. Pat. No. 8,858,201, a rotary push plate is arranged for facilitating fluid flow inside the elastic tube from an inlet to an outlet by pushing a plurality of push pins sequentially. This may prevent friction caused by rotation motion. However, a major drawback of this invention is that the complicated mechanism is created using many moving, wearable parts that increase the likelihood of potential mechanical failure and increase cost of maintenance.